Minus Voltage

http://www.instructables.com/id/How-to-create-voltage-using-one-power-supply/?ALLSTEPS

펠티어(=Peltier) 소자 사용시 필요한 회로이다.

Combine Both 5V and -5V into one of Peltier wires.

and let the other wire not being connected 

go down to GND.